Bifocal lens



H. J. STEAD.

BIFOCAL LEN$.

APPLICATION FILED OCT. 18. 1921.

Patented. Feb. 21, 1922.

UNHTEQ STATES HAROLD J. STEAJ), OF GENEVA, NEW YORK.

- BIFOCAL LENS.

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Application filed October 18, 1921. Serial No. 508,570.

T 0 all whom it may concern:

Be it known that I, HAROLD J. STEAD, of Geneva, in the county of Ontario, in the State of New York, have invented new and useful Improvements in Bifocal Lenses, of which the following, taken in connection with the accompanying drawings, is a full, clear, and exact description.

This invention relates to certain improvements in bifocal lenses.

It has heretofore been proposed to manufacture a bifocal lens in which the two fields of vision are separated by an annular groove. Such a construction has particular advantages in the method of manufacturing, and in avoiding aberration at the separating line or zone between the two fields of vision. But such construction has some disadvantages due to the fact that dirt and other foreign material collects in the groove and it is very difficult to remove the same and the groove becomes very marked in appearance and unsightly, and at times objectionable from the standpoint of vision of the wearer.

The object of this invention, therefore, is to utilize all the manufacturing advantages, while avoiding thedisagreeable features of the groove.

In the drawings Figure 1 is a front view of a lens of my invention.

Figure 2 is a section through the same before the groove is filled.

Figure 3 is a section showing the groove filled.

Figure 4 is an elevation of a blank from which the lenses may be formed.

' Figure 5 is a section through the blank of Figure 4.

The first step in the production of this lens consists in the usual grinding, or generating of the two fields of vision of different dioptrics upon one face of a piece of glass. This piece of glass may be in the form illustrated in Figure 4, from which it is possible to simultaneously grind or generate a suflicient area to constitute two or more lenses when the blank is carefully separated into the desired number of sections.

As illustrated in Figure 4, the blank -1- has two visual surfaces 2-- and 3-, ground thereon with the groove 4- separating the two surfaces. This groove is preferably ground or otherwise formed on the blank after the grinding or production of the two visual surfaces -2- and --3. This groove should preferably be comparatively narrow and comparatively shallow, and the depth and width may be varied within limits to suit the particular conditions at hand. The blank, as illustrated, may be slit along the dotted line shown, and two complete lenses can be formed from a single blank. It will be obvious that the size of theblank may be varied so that one or more lenses may be cut therefrom. The groove 4 may then be filled with a suitable crystalline filling material, -5 such as celluloid, etc., so that the filling material is flush with the two surfaces and forms an unbroken smooth continuation of each. The ground surfaces may then be polished by separate tools, or, the surfaces may be polished prior to the filling of the groove. This latter sequence ofsteps may be preferable in certain cases, but I do not desire to limit myself to any particular sequence of steps.

The result of this method of manufacture is that a lens is produced which can be cheaply and easily produced, and in which the visual surfaces can be made practically perfect without aberration between them, but in which said visual surfaces are separated by the groove filled with a crystalline material, preferably of uncolored transparent character which forms a smooth continuation of the visual surfaces of said lens, so that the surfaces are unbroken and the contour continuous.

By this method, all the advantages of the presence of the groove in the blank are obtained, while the disadvantages of the groove in the finished product are avoided.

' Preferably, the two visual surfaces have their portions bordering the groove upon substantially the same level so that the filling 5- constitutes a substantially level continuation of both of such surfaces. However, it is obvious that such construction is not essential, and that various crystalline filling materials may be used, although such material should preferably be of a transparent nature. Preferably, the groove 4.- is in a roughened, unpolished condition so as to better hold the filling.

Although I have shown and described a particular construction and form and shape of a lens illustrative of an embodiment of Specification of Letters Patent Patented Feb, 21 1922,

my invention, I do not desire to limit myself to the same, as various changes may be made in the structure, form and arrangement without departing from the invention, as set forth. in the appended claims.

lf claim:

1. A bifocal lens having a groove separating the visual surfaces thereof and a filling of material in said groove.

2. A bifocal lens having a groove separat ing the visual surfaces thereof, and a crystalline material filling said groove.

3. A bifocal lens having a groove ground emme between and separating the visual surfaces thereof and material filling said groove.

4. A bifocal lens having a groove ground between and separating the visual surfaces thereof, and a crystalline material filling the groove. 1

In witness whereof I have hereunto set my hand this eighth day of Uctober, 1921.

HAROLD J. srnan 'Witnesses:

MARY C. MURPHY, Lewis E. SPRINGSTEAD, 

